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Meow Bicycle Mechanics and Repair Decal Physics 98/198 spring 2014 Rear Derailleurs.

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meow Bicycle Mechanics and Repair Decal Physics 98/198 spring 2014 Rear Derailleurs


Bicycle Mechanics and Repair DecalPhysics 98/198

spring 2014

Rear Derailleurs



Rear Derailleur

Three Limit Screws

Adjustment Methods• Adjust in quarter turns.• Turning B-screw clockwise increases

tension, pushing the guide pulley further from the sprocket.

• Adjust the H-screw (high limit) when the derailleur is at the smallest (outermost) sprocket.

• Adjust the L-screw when the derailleur is at the largest (innermost) sprocket.

Guide is too far. Need to turn B-Screw Counter-Clockwise

Guide is too close. Need to turn B-Screw Clockwise

Correct distance between guide and sprockets.

Cable Barrel Adjuster

• Look at derailleur and sprockets from the back.

• The chain should be aligned with each sprocket as you shift through the gears.

• If the derailleur is pushing too hard towards the wheel, turn the barrel adjuster clockwise until the chain is aligned.

Aligned Derailleur (Smallest Sprocket).

Derailleur Hanger

Replaceable Hanger

Will sacrifice itself in an accident to keep the frame unharmed.

Non-Replaceable Hanger

Requires special attention and care. A broken hanger is often beyond repair.

The hanger allows the derailleur to be attached to the frame

Repairing a Bent Hanger• If your hanger can be replaced, replace it.• Bend the hanger back with a wrench for

leverage. Be aware, it may still break.

Bent Hanger Repair Option 1 Repair Option 2

Aligning the Derailleur Hanger

• The hunger must be parallel to the rear wheel• If the hanger is straight, but the derailleur

looks bent, replace the derailleur.Resources: http://www.utahmountainbiking.com/fix/rhanger.htmhttp://www.parktool.com/blog/repair-help/rear-derailleur-hanger-alignment

Aligning the Derailleur Hanger

Resources: http://www.utahmountainbiking.com/fix/rhanger.htmhttp://www.parktool.com/blog/repair-help/rear-derailleur-hanger-alignment

Thread in bolt Measure distance(green) to wheel as you rotate the angle


Bend using wrench until distance is the same


Or use the DAG

Pointers on Replacing Cable/Housing• Shift to gear with lowest cable tension.


• Take note of how the cable is mounted before removing it

Pointers on Replacing Cable/Housing• Use the old housing to determine the length

of the new one. Cut to just the right length.

• Cut housing with the correct tool. Make sure the newly-cut edges are not sharp.

Too Long Correct

Fine Adjustment

• A properly tuned derailleur will shift between all front gears and not throw the chain off the chainrings.

• Even a well-adjusted derailleur may rub in some gear combinations

Clockwise = screws adjuster in = loosens cable tension = Moves derailleur inward

Counterclockwise = screws adjuster out = increases cable tension = Moves derailleur outward